troubleshoot-separation

pjt222

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This Claude Skill provides a systematic troubleshooting guide for diagnosing and resolving chromatographic separation issues in GC and HPLC systems. It helps users document symptoms, identify root causes of peak shape and retention anomalies, and evaluate matrix effects. The skill implements targeted fixes using a controlled, one-variable-at-a-time approach for verified corrective actions.

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Troubleshoot Chromatographic Separation

Systematic diagnosis, resolution of GC, HPLC separation problems. Cover symptom documentation, peak shape diagnosis, retention anomaly investigation, matrix effect evaluation, verified corrective action via controlled single-variable changes.

When Use

Peaks tail, front, split, or broader than expected
Retention times shifted or irreproducible
Resolution between critical pairs degraded
Baseline drift, ghost peaks, negative peaks appeared
Sensitivity dropped or signal-to-noise worsened
Method that worked now fails system suitability

Inputs

Required

Problem chromatogram: Current data showing issue
Reference chromatogram: Recent good chromatogram from same method for comparison
Method conditions: Column, mobile phase/carrier gas, temp/gradient, detector, flow rate
System log: Recent maintenance, column changes, mobile phase preparations, instrument events

Optional

Blank chromatogram: Most recent blank or solvent injection
System suitability trend data: Historical values for tailing, resolution, plates, retention time
Column history: Number of injections, types of samples, age of column
Instrument maintenance log: Pump seal replacements, lamp hours, detector service dates

Steps

Step 1: Document Problem

Describe symptom precise — which peaks affected, how differ from reference
Determine when problem started — gradual degradation or sudden onset
Record whether problem affects all peaks or only specific ones
Note whether problem present in standards, samples, or both
Collect current system suitability data, compare to historical trends
Photograph or export problem chromatogram alongside reference for side-by-side comparison

Got: Documented problem statement with timeline, scope (all peaks vs. specific peaks, standards vs. samples), comparison to reference data.

If fail: No reference chromatogram? Inject fresh standard preparation under documented method conditions. Establish current baseline before troubleshooting.

Step 2: Diagnose Peak Shape Issues

Use symptom table to identify likely root causes.

Symptom	Possible Causes	Solutions
Tailing (T > 1.5)	Secondary interactions (silanol activity), dead volume in fittings, contaminated column frit, overloaded active sites	Add amine modifier (HPLC), deactivate liner (GC), replace frit, trim column inlet, reduce injection mass
Fronting (T < 0.8)	Column overload (mass or volume), mismatch between sample solvent and mobile phase strength	Reduce injection volume or concentration, dilute in weaker solvent, use larger-bore column
Split / double peaks	Partially blocked frit, void at column head, two polymorphic forms, isomeric interconversion	Replace frit, repack column head, verify sample stability, adjust pH to lock one form
Broad peaks (all)	Extra-column band broadening, wrong tubing ID, large detector cell, old column, low plate count	Minimize post-column tubing length and ID, check connections, replace column
Broad peaks (early eluters)	Poor focusing at column head, injection solvent too strong (HPLC), cold on-column (GC)	Use weaker injection solvent, reduce injection volume, increase initial oven temp
Broad peaks (late eluters)	On-column diffusion, temperature too low (GC), insufficient gradient steepness (HPLC)	Increase final oven temperature, steepen gradient, add organic wash
Negative peaks	Sample solvent refractive index/absorbance differs from mobile phase, vacancy peaks (IEX)	Match sample solvent to mobile phase, use different detection wavelength
Ghost peaks	Carryover from previous injection, contaminated mobile phase, column bleed, septum bleed (GC)	Run blank to confirm, clean or replace injection system, filter/degas mobile phase, replace septum
Baseline drift (upward)	Column bleed (GC at high temp), gradient elution baseline shift (HPLC), lamp instability (UV)	Reduce max temp, use low-bleed column (GC), run blank gradient to characterize (HPLC), replace lamp
Baseline noise (high-frequency)	Electrical interference, pump pulsation, air bubbles in detector, contaminated detector	Ground instrument, replace pump seals, degas mobile phase, clean detector cell

Match observed symptom(s) to table above
Narrow list of causes — check whether problem affects all peaks or specific ones, whether appeared sudden or gradual
Prioritize most likely cause based on system history (recent changes, column age, maintenance status)

Got: One or two most-likely root causes identified from symptom-cause mapping. Prioritized by system history.

If fail: Symptom matches no row, or multiple symptoms simultaneous? Problem may be compound (e.g., column degradation plus leak). Address most obvious issue first. Re-evaluate.

Step 3: Diagnose Retention Time Issues

Symptom	Possible Causes	Solutions
All peaks shifted earlier	Increased flow rate, higher column temperature, stronger mobile phase, column void	Check flow rate setting and actual delivery, verify temperature, remake mobile phase, inspect column
All peaks shifted later	Decreased flow rate, lower column temperature, weaker mobile phase, partially blocked tubing	Check for leaks (pressure drop), verify temperature, remake mobile phase, check inline filter
Retention time drift (gradual)	Column degradation, mobile phase evaporation (open reservoir), temperature fluctuation	Replace column, seal reservoir, stabilize oven, use column thermostat
Retention time irreproducible	Leak at fitting, check valve malfunction, autosampler timing error, inadequate re-equilibration	Pressure-test fittings, replace check valves, verify autosampler, increase equilibration volume
Lost retention (k' near 0)	Phase collapse (RP at high aqueous), column dewetting, wrong mobile phase, reversed connections	Use polar-embedded or AQ-type column, re-wet column with organic, verify mobile phase, check plumbing
Co-elution (previously resolved)	Column selectivity lost (bonded phase stripped), mobile phase composition changed, temperature changed	Replace column, verify mobile phase preparation, check temperature setpoint vs. actual

Determine whether retention shifts uniform (all peaks) or selective (specific peaks)
Uniform shifts → systematic causes (flow, temp, mobile phase composition)
Selective shifts → column chemistry changes or specific analyte-related issues
Check instrument pressure trace — sudden pressure changes indicate leaks or blockages
Re-inject reference standard to confirm whether issue in system or sample

Got: Root cause of retention anomaly identified, categorized as systematic (instrument/mobile phase) or column-related.

If fail: Re-inject standard on new column resolves issue? Original column the problem. Issue persists on new column? Cause upstream (mobile phase, instrument, method parameters).

Step 4: Evaluate Matrix Effects

Compare standard chromatogram to sample chromatogram:
- Additional peaks in sample absent in standard?
- Baseline elevated or noisy in specific retention windows?
- Analyte peak shapes different in sample vs. standard (broader, tailing more)?
For LC-MS — evaluate ion suppression/enhancement:
- Post-column infusion test — infuse analyte continuous while inject blank matrix extract. Dips in analyte signal indicate ion suppression regions
- Analyte retention time coincides with suppression region? Modify method to shift analyte elution
Check column contamination:
- Inject solvent blanks after sample sequence. Persistent peaks indicate column contamination
- Flush column with strong solvent (100% organic for RP, or as recommended by column manufacturer)
Assess sample preparation:
- Dirty injector (autosampler needle, injection port liner in GC) — replace or clean
- Insufficient sample cleanup — add filtration, SPE, or protein precipitation step
For GC — check non-volatile residue buildup in inlet liner. Causes peak tailing, ghost peaks over time.

Got: Matrix effects characterized (presence/absence of interferents, ion suppression zones for LC-MS, column contamination status). Actionable recommendations.

If fail: Matrix effects can't be characterized adequately with available data? Prepare matrix-matched calibration curve. Compare slopes to solvent calibration curve. Slope difference > 15% indicates significant matrix effects requiring method modification.

Step 5: Implement and Verify Fix

Change one variable at a time. Document what changed and why
After each change, re-inject system suitability standard. Compare to reference chromatogram
Sequence of changes (least to most disruptive):
- Prepare fresh mobile phase / carrier gas tank
- Replace consumables (septum, liner, frit, inline filter, lamp)
- Tighten or replace fittings, tubing
- Flush/regenerate column
- Adjust method parameters (temp, flow, gradient, pH)
- Replace column
- Service instrument (pump seals, check valves, detector)
Once fix identified, run full system suitability test (n >= 5 injections)
Compare all parameters (retention time, area, resolution, tailing, plates) to historical specification
Document root cause, corrective action, verification results in instrument/column logbook
Same problem recurs? Establish preventive maintenance schedule. Address root cause proactive

Got: Problem resolved. System suitability parameters restored to specification. Root cause, corrective action, verification documented.

If fail: All single-variable changes fail to resolve issue? Problem may involve multiple simultaneous failures. Replace all consumables and column together. Verify with fresh standard. Rebuild troubleshooting from new baseline. Problem persists after total consumable replacement? Escalate to instrument service.

Checks

Problem documented with symptom description, timeline, scope
Root cause identified using symptom-cause mapping tables
One variable changed at a time during troubleshooting
Fix verified by system suitability test (n >= 5 replicate injections)
All system suitability parameters restored to within specification
Root cause, corrective action documented in logbook
Preventive measure identified to avoid recurrence

Pitfalls

Change multiple variables simultaneous: Makes impossible to identify actual root cause. Always change one thing, test, then decide whether to change another
Replace column as first step: Column replacement expensive. May mask real problem (leak, wrong mobile phase, contaminated inlet). Exhaust simpler possibilities first
Ignore instrument logbook: Many problems trace back to recent maintenance event, mobile phase batch change, column swap. Always check what changed recent
Blame sample without evidence: Run reference standard first. Standard also shows problem? Issue in system, not sample
Flush column with incompatible solvents: Never flush reversed-phase column with pure water (causes phase collapse) or silica HILIC column with pure aqueous buffer (irreversible damage). Follow manufacturer washing protocol
No document what tried: Failed troubleshooting attempts valuable info. Record every change attempted, outcome. Avoid repeat unsuccessful fixes. Build institutional knowledge

GitHub 仓库

pjt222/agent-almanac

路径: i18n/caveman/skills/troubleshoot-separation

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